LONDON — John McDonnell has called on Theresa May to prove she has "nothing to hide" and declare her tax returns, after more than 10,000 people signed a petition calling on MPs to debate whether the prime minister should disclose whether she has any offshore interests.

Both the PM and her husband have money invested in a shared "blind trust" which could contain offshore investments, while Philip May works for a company that was linked to the Panama Papers tax avoidance scandal.

May has so far refused to publish her tax return since becoming prime minister, with a spokesperson insisting earlier this year that there is "no long-standing convention" for the prime minister to do so.

The Shadow Chancellor today urged May to prove she has nothing to hide on the matter.

"John and Jeremy [Corbyn] both publish their tax returns in full every year unlike the Chancellor and the Prime Minister who only publish an edited version," a spokesperson for McDonnell told Business Insider.

"The simplest way for them to avoid any suggestions that they would have something to hide is to just be as transparent as possible."

McDonnell's comments came after more than 10,000 people signed an e-petition calling on Parliament to debate whether the prime minister should disclose any offshore interests held by her and her husband, Philip.

The petition had received 10,328 signatures at the time of writing, meaning May's government must formally respond to it. The governments are obliged to respond to all petitions which receive 10,000 signatures or more.

The petition was created by Barrister Jolyon Maugham following the Labour Party telling Business Insider last month that Philip had "serious questions to answer" after the company May works for was linked to the Panama Papers scandal.

Leaked emails seen by Private Eye suggest that investment advisors Capital Group, where Mr May is a relationship manager, used offshore law firm Appleby to arrange investments in tax havens.

"There are some serious questions for Philip May to answer about his firm's use of tax havens, whether he had any knowledge of it and if he thinks this is an acceptable way to do business," Labour's Shadow Minister for the Cabinet Office, Jon Trickett, told BI last month.

In a statement to BI, Maugham said: "This is pretty poor stuff from Theresa May.

"Even her predecessor recognised the need to be straight with the public about what offshore assets he held. Theresa May's stance is effectively to thumb her nose at legitimate public concern."

A spokesperson for the prime minister told Business Insider last month that the PM had no "direct" investments offshore.

"Neither the prime minister nor Mr May have any direct offshore investments," her spokesperson said.

Asked by Business Insider today about Labour's calls for her to publish her tax return, a spokesperson for May said that she had previously published her tax returns during the Conservative leadership election and added: "Her financial settlements are set out in terms of her blind trust which we have discussed before."

The petition https://petition.parliament.uk

PM under pressure to be more transparent

The use of a blind trust raises the possibility that the Mays could have money invested offshore without their knowledge.

Asked about this last month, the PM's spokesperson replied: "The nature of a blind trust is just that.

"It is a well-established mechanism for protecting ministers in their handling of interests and it means they are not involved in any decisions on the management, acquisitions or disposal of items in the trust. By definition a blind trust is blind."

Asked by BI whether the prime minister had requested that the blind trust was ethical in terms of tax, they replied that they "have nothing more to add," on the matter.